Having such releases, with clear version numbers, make it easier for the distributions (Linux OS) to have a common version of this excellent tool, where as the other tools depending on FFmpeg can (ideally) rely on these versions.
Incidentally, the version of Mplayer (1.0rc3) which was supposed to come out a year ago, just came out two weeks ago. Please note that the first release candidate was published around October 2006 and second around October 2007.
In general if you wish to develop something with these tools, use their code which is under version control, that is where there progress is being made.
svn checkout svn://svn.ffmpeg.org/ffmpeg/trunk ffmpeg
svn checkout svn://svn.mplayerhq.hu/mplayer/trunk mplayer